2. Groups of "real" qualities in an extra-mental world, more or less like what is immediately known.
3. Substance; the "I know not what" to which Locke clung through all difficulties.
The man who holds the first of the three views above mentioned need only consider the first and the second of these; and the Kantian need only consider the first and the third, rebaptizing the latter "noumenon" or "thing-in-itself."
Omitting for later consideration the sameness of the self or ego, I have already discussed the uses of the word same within the field of the immediately known. It remains to consider the sameness of what is believed to lie beyond this, and to belong to a different kind of a world.
When men discuss these supposed realities, in what senses of the word same may they reasonably think of them as the same?
When a common, unreflective man, whose mind has not been, in the words of Bishop Berkeley, "debauched by learning," looks at a tree and thinks about it, he believes he sees a real tree, at a certain real distance from his body, and of a given real height and figure. It does not occur to him to make any distinction between the tree immediately perceived, and an inferred second tree, not immediately perceived, but represented by the former. There is the tree; he sees it; he can touch it; it seems to him but one: and he always talks as if there were but one tree to be discussed in the premises. That one tree, he thinks, is really extended; is really out in space beyond his body; is, in short, what it appears to be. To his unreflective mind this tree does not seem to be a representative or to be seen through a representative, but to be seen immediately and just where it really is.
But when a man has begun to battle with the difficulties of reflection, and has learned to make a distinction between things and his ideas of the things, he will probably fall into unforeseen perplexities about this tree. He reflects that, when he closes his eyes, the tree disappears; that when he approaches it it looks green, and when he recedes from it it grows blue; that a man with a peculiar defect in his vision does not see it colored as he does; that when he makes a pressure on the side of one eyeball he sees two trees where before he saw only one; that when he makes such a pressure upon both eyeballs and moves them about a little he sees two trees moving about, although he knows real trees can not ordinarily be made to move about so easily. Such reflections lead him to distinguish between the tree as he sees it, and the tree as it really is, and he defines the tree as he sees it as the tree immediately known, and the real tree as the tree mediately known, a cause of the existence of the former. He now thinks that he sees directly only copies or representatives of real things, and as he believes these copies or representatives to be in his mind, and usually talks as if his mind were in his head, or at least in his body, he concludes that things immediately known must in many instances be much smaller than they seem, or perhaps lack extension altogether. How can a tree thirty feet high be in a man's mind? It is true, that, when I press upon my eyeballs in the manner described, I seem to see two trees of that size moving; but must it not be a mistake? Must we not assume that what is immediately seen only seems extended, and stands for an extended thing which is grasped through it? So our philosopher learns to distrust the immediate object of knowledge; to regard it as in some sense unreal as compared with what it represents; and to deny to it those properties which it apparently possesses. It is not extended, but it stands for extension; it is not colored, but it stands for color; it is not real, but it stands for reality.
It is natural, however, for one who has gone thus far to go farther. When he reflects again upon the fact that he sees the tree of a different color at different distances; when he remembers that colors vary with the quality of the light by which they are seen; when he and his neighbor dispute concerning the true color of the one tree which he sees dotted with red leaves, and which his opponent claims to see of a uniform color; then he may well begin to ask himself what is the true color of the "real" tree, or whether it is certain that it has any color at all? May not, then, the "real" tree have only some of the qualities that we ordinarily attribute to trees? Perhaps, the space qualities?
Or, worse yet, since some of the qualities that the ordinary man attributes to trees may be regarded as existing only in a shadowy way in our ideas, why may not the same be true of all the other qualities? How do we know that "real" trees are extended? How do we know that "real" extension must be assumed as the cause of the delusive apparent extension of our ideas, if it is true that "real" color need not thus be assumed as a cause of our sensations of color? What if the "real" thing exists only as an indescribable and incomprehensible somewhat, which we must assume as a cause of the immediately known, but of which we can know nothing more? When one has once begun this slippery descent, it is not easy to say where he may find a peg to stay him in his course.
Suppose, however, he is content to strip the "real" thing of what are commonly called the secondary qualities of matter, and to leave to it what are known as the primary. He will follow the example of the wholly unreflective man and speak of it in such a way as to suggest that the thing itself is something apart from its "real" qualities. A tree, he will say, has qualities. It would certainly sound odd to hear him say it is qualities. And he will very possibly go on to justify the use of the language he employs by distinguishing between the "real" qualities represented by his mental picture of the tree and an obscure something which he assumes as underlying them; thus embracing the Lockian distinction of ideas, "real" qualities, and substance. He may conclude, it is true, that substance in this sense of the word is chimerical, and that the belief in it arises out of a misunderstanding of the significance of language; but if he has gone so far as to assume duplicates of things immediately known, in the form of "real" qualities, it is more probable that he will be inclined to complete his classes of beings by adding the third.[4]